Structure and phase transition features of monoclinic and tetragonal phases in U–MO alloys

Abstract

Using molecular dynamics simulations, we studied the structural properties of orthorhombic, monoclinic, and body-centered tetragonal (bct) phases of U–Mo alloys. A sequence of shear transformations between metastable phases takes place upon doping of uranium with molybdenum from pure α-U: orthorhombic α′ → monoclinic α′′ → bct γ0 → body-centered cubic (bcc) with doubled lattice constant γs → bcc γ. The effects of alloy content on the structure of these phases have been investigated. It has been shown that increase in molybdenum concentration leads to an increase in the monoclinic angle and is more similar to the γ0-phase. In turn, tetragonal distortion of the γ0-phase lattice with displacement of a central atom in the basic cell along the <001> direction makes it more like the α′′-phase. Both of these effects reduce the necessary shift in atomic positions for the α′′ → γ0-phase transition.